something of AD8402R10

The AD8400AR10/AD8402R10/AD8403AR10 provide a single, dual or quad
channel, 256 position digitally controlled variable resistor (VR)
device. These devices perform the same electronic adjustment
function as a potentiometer or variable resistor. The AD8400AR10
contains a single variable resistor in the compact SO-8 package.
The AD8402AR10 contains two independent variable resistors in
space saving SO-14 surface mount package. The AD8403AR10 contains
four independent variable resistors in 24-lead PDIP, SOIC
and TSSOP packages. Each part contains a fixed resistor with a
wiper contact that taps the fixed resistor value at a point determined
by a digital code loaded into the controlling serial input
register. The resistance between the wiper and either endpoint
of the fixed resistor varies linearly with respect to the digital
code transferred into the VR latch. Each variable resistor offers
a completely programmable value of resistance, between the A
terminal and the wiper or the B terminal and the wiper. The
fixed A to B terminal resistance of 1 kW, 10 kW, 50 kW or 100 kW
has a ±1% channel-to-channel matching tolerance with a nominal
temperature coefficient of 500 ppm/°C. A unique switching circuit
minimizes the high glitch inherent in traditional switched
resistor designs avoiding any make-before-break or break-beforemake
operation.
Each VR has its own VR latch that holds its programmed
resistance value. These VR latches are updated from an SPI
compatible serial-to-parallel shift register that is loaded from a
standard 3-wire serial-input digital interface. Ten data bits make
up the data word clocked into the serial input register. The data
word is decoded where the first two bits determine the address
of the VR latch to be loaded, the last eight bits are data. A serial
data output pin at the opposite end of the serial register allows
simple daisy-chaining in multiple VR applications without additional
external decoding logic.